Graphs and NetworksMaps

The four colour theorem is the first well-known mathematical theorem to be proven using a computer, something that has become much more common and less controversial since. Faster computers and a more efficient algorithm mean that today you can prove the four colour theorem on a laptop in just a few hours.

Postmark for the Department of Mathematics at the University of
Illinois Urbana-Champaign, where Haken and Appel worked.